Microsoft released MS08-067 security patch on Thursday, rated as critical.

This security update resolves a vulnerability in the Server service that affects all currently supported versions of Windows. Windows XP and older versions are rated as critical while Windows Vista and newer versions are rated as important. Because the vulnerability is potentially wormable on those older versions of Windows Microsoft is encouraging customers to test and deploy the update as soon as possible.

In addition, to releasing a security update to address the vulnerability, Micrisoft said that it had taken steps to help enable broader protections for customers.

Microsoft said that they had discovered this vulnerability as part of their research into a limited series of targeted malware attacks against Windows XP systems that they discovered about two weeks ago through their ongoing monitoring.

"As we investigated these attacks we found they were utilizing a new vulnerability and initiated our Software Security Incident Response Process (SSIRP). As we analyzed the vulnerability in our SSRP process, we found that this vulnerability was potentially wormable on Windows XP and older systems," Microsoft said. "Our analysis also showed that it would be possible to address this vulnerability in a way that would enable us to develop an update of appropriate quality for broad distribution quickly," the company added.